Low-Temperature Coolant Cooler

ABSTRACT

The invention relates to a low-temperature coolant cooler, for the indirect charge-air cooling on an internal combustion engine, with a number of flat tubes, through which 700 to 1,800 litres per hour of coolant flow during operation, which open out in coolant collectors ( 4,8 ) and air guide devices, in particular, air guide fins are arranged between the flat tubes around which charge air for cooling flows. In order to guarantee a constant cooling power over a large operating range of coolant throughput, said low-temperature coolant cooler comprises the following features: a) the flat tubes have a depth ( 23 ) of less than or equal to 20 millimetres, b) the coolant flowing through the flat tubes is deflected a maximum of two times in the collectors ( 4, 8 ) and c) the flat tubes are provided with internal turbulence generating devices.

The invention relates to a low-temperature coolant cooler for theindirect charge-air cooling of an internal combustion engine, having aplurality of flat tubes which, in operation, are traversed by 700 to1800 liters of coolant per hour and open out into coolant collectingtanks, with air guide devices, in particular air guide plates, beingarranged between the flat tubes, around which air guide plates flowscharge air which is to be cooled.

In charge air coolers for internal combustion engines, the charge airwhich is to be cooled can reach temperatures of up to 220 degreesCelsius or higher. On account of the high temperatures, damage can occurat the inlet side of the cooler. For this reason, the German laid-openspecification DE 199 62 391 A1 proposes a charge air cooler which ischaracterized by at least two cooling circuits with different coolanttemperatures, which cooling circuits are each guided by heat exchangerblocks which are connected in series in the flow direction of the air.The known charge air cooler comprises a pre-cooler, a high-temperaturecharge air cooler and a low-temperature charge air cooler. Thelow-temperature charge air cooler receives coolant via a separatelow-temperature circuit, and is therefore also referred to as alow-temperature coolant cooler. Upon entering the low-temperaturecoolant cooler, the coolant is for example at a temperature of 45 to 60degrees Celsius. The low-temperature circuit is for example driven by anelectric coolant pump which is also referred to as a low-temperaturecoolant pump. The coolant throughput of the low-temperature coolantcooler is relatively low and is around 700 to 1800 liters per hour.Known low-temperature coolant coolers have flat tubes which are smoothon the inside. In order to obtain sufficient flow speeds for theinternal heat transfer, three or more deflections are necessary in thecase of flat tubes which are smooth on the inside.

It is an object of the invention to provide a low-temperature coolantcooler for the indirect charge air cooling of an internal combustionengine, having a plurality of flat tubes which, in operation, aretraversed by 700 to 1800 liters of coolant per hour and open out intocoolant collecting tanks, with air guide devices, in particular airguide plates, being arranged between the flat tubes, around which airguide plates flows charge air which is to be cooled, whichlow-temperature coolant cooler ensures a constant cooling capacity overa wide operating range of the coolant throughput.

The object is achieved in a low-temperature coolant cooler for theindirect charge air cooling of an internal combustion engine, having aplurality of flat tubes which, in operation, are traversed by 700 to1800 liters of coolant per hour and open out into coolant collectingtanks, with air guide devices, in particular air guide plates, beingarranged between the flat tubes, around which air guide plates flowscharge air which is to be cooled, by the following features: the flattubes have a depth which is less than/equal to 20 millimeters; thecoolant which traverses the flat tubes is deflected a maximum of twotimes in the collecting tanks; and the flat tubes are equipped at theinside with turbulence-generating devices. During operation, air flowsaround the air guide devices which are arranged between the flat tubes,which air extracts heat from the coolant in the interior of the flattubes. The extent of the flat tubes in the air throughflow direction ofthe air guide devices is referred to as the depth of the flat tubes.Known low-temperature coolant coolers are equipped with flat tubes whichare smooth on the inside. In order to obtain sufficient flow speeds forthe internal heat transfer, three or more deflections are necessary inthe collecting tanks. Within the context of the present invention, itwas found that a coolant-side pressure drop observed in knownlow-temperature coolant coolers is to be attributed to a pronouncedeffect of the coolant viscosity and therefore ultimately to the ambienttemperature. Together with a flat pump characteristic curve, the resultis a strong dependency of the coolant throughput and the capacity on theambient temperature. Despite multiple deflections, the flow in the knownlow-temperature coolant coolers with smooth on the inside tubes islaminar, or in the transition region, laminar to turbulent. The capacityof the known low-temperature coolant coolers is therefore stronglydependent on the coolant throughput. This can result, in particular atvery low temperatures, in the pressure build-up of the low-temperaturecoolant pump being insufficient on account of the high resistance in thelow-temperature coolant cooler. With the design according to theinvention of the low-temperature coolant cooler, it is possible tomaintain an approximately constant cooling capacity over a wideoperating range of coolant throughput. This considerably diminishes theeffects of the ambient temperature and of tolerances on the charge aircooling.

One preferred exemplary embodiment of the low-temperature coolant cooleris characterized in that the flat tubes with the turbulence-generatingdevices are designed in such a way that the ratio between the maximumand minimum pressure loss in the flat tubes is less than 3 for a coolantthroughput of 700 to 1800 liters per hour. This provides a fasterresponse of the indirect charge air cooling at low ambient temperatures.

A further preferred exemplary embodiment of the low-temperature coolantcooler is characterized in that the ratio between the maximum andminimum Nusselt number in the flat tubes is less than 3 for a coolantthroughput of 700 to 1800 liters per hour. The Nusselt number iscalculated from the ratio between the product of the heat transfercoefficient and a characteristic length, and the thermal conductivity ofthe material used. The material used is preferably aluminum sheet.

A further preferred exemplary embodiment of the low-temperature coolantcooler is characterized in that the flat tubes have inwardly alignedindentations on at least one of their flat sides. The indentations arepreferably formed corresponding to the exemplary embodiments which aredisclosed in the German laid-open specification DE 101 27 084 A1.

A further preferred exemplary embodiment of the low-temperature coolantcooler is characterized in that turbulence inserts are arranged in theflat tubes. The turbulence inserts are preferably equipped with similarindentations to the flat tubes described above.

Further advantages, features and details of the invention can begathered from the following description, in which various exemplaryembodiments are described in detail with reference to the drawing. Here,the features mentioned in the claims and in the description can beessential to the invention in each case individually or in any desiredcombination. In the drawing:

FIG. 1 is a schematic, perspective illustration of a low-temperaturecoolant cooler according to a first exemplary embodiment;

FIG. 2 is a similar illustration to that in FIG. 1, according to afurther exemplary embodiment;

FIG. 3 shows a Cartesian coordinate diagram in which the charge airtemperature downstream of the charge air cooler is plotted against thecoolant throughput;

FIG. 4 shows a Cartesian coordinate diagram in which the coolantpressure is plotted against the coolant throughput, and

FIG. 5 shows a Cartesian coordinate diagram in which the Nusselt numbernormalized to a minimum Nusselt number, or the pressure loss normalizedto a minimum pressure loss, in the cooler network is plotted against thecoolant throughput.

FIG. 1 is a schematic perspective illustration of a low-temperaturecoolant cooler 1 according to the invention. The low-temperature coolantcooler 1 comprises an upper collecting tank 4, on which is provided aninlet connecting pipe 5 for coolant. An arrow 6 indicates the coolantentering into the upper collecting tank 4. The coolant throughputthrough the low-temperature coolant cooler 1 according to the inventionis greater than 0.2 and less than 0.5 kg/s.

The low-temperature coolant cooler 1 also has a lower collecting tank 8,on which is provided an outlet connecting pipe 9 for the coolant. Thecoolant passing out of the lower collecting tank 8 is indicated by anarrow 10. The coolant is preferably water with special additives.

Provided between the upper collecting tank 4 and the lower collectingtank 8 is a heat exchanger block 12 which comprises a plurality of flattubes (not illustrated) which run between the collecting tanks 4 and 8,which are also referred to as coolant collecting tanks. Air guideplates, for example in the form of corrugated fins, are arranged betweenthe flat tubes, around which air guide plates flows charge air which isto be cooled.

Arranged in the upper collecting tank 4 is a first partition 17, bymeans of which the coolant which enters into the low-temperature coolantcooler 1 through the inlet connecting pipe 5 is deflected for a firsttime along an arrow 18. Arranged in the lower collecting tank 8 is asecond partition 20, by means of which the coolant is deflected for asecond time in the low-temperature coolant cooler 1 along an arrow 21,before exiting the low-temperature coolant cooler 1 through the outletconnecting pipe 9.

The low-temperature coolant cooler 1 is preferably made from aluminumsheet and has a depth 23 of less than/equal to 20 millimeters.Advantageously under some circumstances, the low-temperature coolantcooler according to the invention has a greater width than height, asillustrated by way of example in FIG. 1.

FIG. 2 is a schematic, perspective illustration of a low-temperaturecoolant cooler 31. The low-temperature coolant cooler 31 comprises aleft-hand collecting tank 34 which is equipped with an inlet connectingpipe 35. Coolant enters into the left-hand collecting tank 34 throughthe inlet connecting pipe 35 as indicated by an arrow 36. The massthroughput of coolant is greater than 0.2 and less than 0.5 kg/s. Inaddition, the left-hand collecting tank 34 is provided with an outletconnecting pipe 38. The coolant passes out of the low-temperaturecoolant cooler 31 through the outlet connecting pipe 38.

In addition, the low-temperature coolant cooler 31 has a right-handcollecting tank 42. Formed between the left-hand collecting tank 34 andthe right-hand collecting tank 42 is a heat exchanger block 44. The heatexchanger block 44 comprises a plurality of flat tubes (not illustrated)which run in the horizontal direction between the left-hand collectingtank 34 and the right-hand collecting tank 42. Arranged between the flattubes are air guide plates, for example in the form of corrugated fins,around which flows charge air which is to be cooled.

Provided in the left-hand collecting tank 34 is a first partition 48, bymeans of which the coolant which enters into the low-temperature coolantcooler 31 through the inlet connecting pipe 35 is deflected a singletime along an arrow 49, before exiting through the outlet connectingpipe 38. The low-temperature coolant cooler 31 illustrated in FIG. 2 hasa depth 51 of at most 20 millimeters.

The low-temperature coolant coolers illustrated in FIGS. 1 and 2 have ineach case an installation depth of at most 20 millimeters. The flattubes of the low-temperature coolant coolers are equipped withturbulence-generating surfaces as are disclosed in FIGS. 2 to 8 of theGerman laid-open specification DE 101 27 084 A1, or withturbulence-generating inserts which are also referred to as turbulators,and with a maximum of two deflections. This provides that the ratio ofthe pressure loss in the tubes at a minimum/maximum mass flow rate (0.2kg/s<mass flow rate <0.5 kg/s) is less than 3. At the same time, theNusselt number varies at most by a factor of 3 between the maximum andminimum coolant throughput.

As illustrated by way of example in FIG. 2, it is under somecircumstances advantageous for the low-temperature cooler according tothe invention to have a width which is smaller than its height. Here,the height is the dimension in the tube longitudinal direction.

In FIG. 3, the charge air temperature downstream of the coolant-cooledcharge air cooler in degrees Celsius is plotted against the coolantthroughput in kg/s. The effect of the design according to the inventionon the charge air cooling is illustrated on the basis of variouscharacteristic curves. The charge air cooling for coolers without aturbulence-enhancing tube inner side, with a laminar tube flow or a tubeflow in the deflection region between laminar and turbulent, isillustrated on the basis of two characteristic curves 53. 54 denotes aregion which is to be avoided on account of undesired boiling in thecoolant-cooled charge air cooler. 56 denotes a characteristic curve of alow-temperature coolant cooler according to the invention, which is alsoreferred to as a charge air cooler. The low-temperature coolant cooleraccording to the invention is equipped with a turbulence-enhancing tubeinner side. This ensures improved and approximately constant charge aircooling over a wide coolant throughput range. 58 and 59 denote operatingpoints with a tolerance-induced scatter band.

In FIG. 4, the coolant pressure in bar is plotted against the coolantthroughput in kg/s. 62 denotes a pump characteristic curve. 64 to 67denote various system characteristic curves of a heat exchangeraccording to the invention (64, 65) and of a known heat exchanger (66,67). The system characteristic curve 64 corresponds to an ambienttemperature of 35 degrees Celsius. The associated system characteristiccurve 65 corresponds to an ambient temperature of −5 degrees Celsius.The system characteristic curve 66 in turn corresponds to an ambienttemperature of 35 degrees Celsius. The associated system characteristiccurve 67 corresponds to an ambient temperature of −5 degrees Celsius.FIG. 4 shows an advantageous reduction, by means of the presentinvention, of the pressure required for a desired coolant throughput.

70 denotes the difference in the coolant throughput at the differentambient temperatures in a design according to the prior art. Since thetemperature influence on the coolant throughput is very high in a designaccording to the prior art, the difference 70 is likewise very high. 71denotes the difference in the mass throughputs at different temperaturesin a design according to the invention with a turbulence-enhancinginner, side. A comparison between 70 and 71 makes it clear that thetemperature influence can be considerably reduced by means of the designaccording to the invention.

In FIG. 5, the Nusselt number normalized to a minimum Nusselt number, orthe pressure loss normalized to a minimum pressure loss, in the flattubes is plotted against the coolant throughput. Since all of theplotted variables rise continuously with increasing coolant throughput,and are a minimum at 0.2 kg/s, all of the curves begin at 0.2 kg/s withthe value 1.

74 denotes the normalized Nusselt number for smooth tubes with threedeflections. 75 denotes the normalized pressure loss for smooth tubeswith three deflections. 76 denotes the normalized pressure loss for adesign according to the invention with one deflection. 77 denotes thenormalized Nusselt number for the new design with one deflection. FIG. 5shows that the influence of the coolant quantity on the heat transferfunction and on the coolant-side pressure loss can be reduced by meansof the measures according to the invention.

1. A low-temperature coolant cooler for the indirect charge air coolingof an internal combustion engine, comprising a plurality of flat tubeswhich, in operation, are traversed by 700 to 1800 liters of coolant perhour and are connected to coolant collecting tanks, and air guidedevices arranged between the flat tubes, around whereby charge air whichis to be cooled flows the air guide devices for cooling wherein: a) theflat tubes have a depth which is less than/equal to 20 millimeters; b)the coolant which traverses the flat tubes changes flow direction amaximum of two times in the collecting tanks; and c) the flat tubes areequipped at the inside with turbulence-generating devices.
 2. Thelow-temperature coolant cooler as claimed in claim 1, wherein the flattubes with the turbulence-generating devices are designed in such a waythat the ratio between the maximum and minimum pressure loss in the flattubes is less than 3 for coolant throughputs of 700 to 1800 liters perhour.
 3. The low-temperature coolant cooler as claimed in claim 2,wherein the ratio between the maximum and minimum Nusselt number in theflat tubes is less than 3 for coolant throughputs of 700 to 1800 litersper hour or of 0.2 to 0.5 kg/s.
 4. The low-temperature coolant cooler asclaimed in claim 1, wherein the flat tubes have inwardly alignedindentations on at least one of their flat sides.
 5. The low-temperaturecoolant cooler as claimed in claim 1, wherein turbulence inserts arearranged in the flat tubes.
 6. The low-temperature coolant cooler asclaimed in claim 2, wherein the flat tubes have inwardly alignedindentations on at least one of their flat sides.
 7. The low-temperaturecoolant cooler as claimed in claim 3, wherein the flat tubes haveinwardly aligned indentations on at least one of their flat sides. 8.The low-temperature coolant cooler as claimed in claim 2, whereinturbulence inserts are arranged in the flat tubes.
 9. Thelow-temperature coolant cooler as claimed in claim 3, wherein turbulenceinserts are arranged in the flat tubes.
 10. The low-temperature coolantcooler as claimed in claim 4, wherein turbulence inserts are arranged inthe flat tubes.